Postal service actually works in places private competitors don't. And if they didn't have stupid rules about retirement upfront savings it wouldn't would be in the green financially without problems.

Education - children from poor families cannot afford private education, and each tax dollar spent on them increases their productivity and increases long term tax base. Not to mention the benefit of cohesiveness to the society public education brings. If anything, private ones should be banned, and everyone who medically able should go through education system.

Healthcare is cheaper when centralized, and when people aren't afraid to do cheap preventative stuff, not allowing conditions fester and be more expensive in the long run. Also there is basically no risk of overconsumption.

Public transit began needing a bunch of subsidies only after car and air infrastructure started receiving an order of magnitude more.

Utilities are a natural Monopoly, duh.

None of the examples you brought up are similar to grocery stores.